Here’s a quick guide to obtaining your very own Witcher Viper set that was added in the Hearts of Stone expansion pack. This set includes both armor and two swords.
This medium armor set is themed around poison, so it has high poison resistance and the swords have a chance to poison on attack. The armor looks like a recolored version of the gear you start the game with.
How to get the Viper Armor
The four Diagrams for the Viper armor can only be obtained during the beginning of the Heist mission, when you are inside Vivaldi’s auction house. They are sold by Countess Mignole.
How to get the Viper Venomous Steel Sword
The Steel Sword diagram can be found inside Borsodi’s vault during the Heist mission, in the final room.
How to get the Viper Venomous Silver Sword
The Silver sword can only be found if you choose the “Help Olgierd” option during the ending of the expansion. You can then find the sword directly (no diagram required) inside the shadowy realm that Gaunter O’Dimm puts you in. From the starting area, go straight down, then across the bridge, and then go left down the path.
After following the path, you should see some stairs leading up to an area with a red glow around it; jump up the broken stairs and you will find the sword inside a rock.